This application is a resubmission of research originally proposed in response to NIDA PA-07-111 Behavioral & Integrative Treatment Development Program (RO1), and presently to the NIH-RO1-FOA. Co-occurring substance use and psychiatric disorders are common in the general population, even more prevalent in clinical settings, and associated with negative treatment and life outcomes. Posttraumatic stress disorder (PTSD) is among the most widespread of co-occurring disorders, vexing to clinicians, and a risk factor for attrition, relapse to drugs and alcohol, and deterioration in psychiatric symptoms. There have been several behavioral therapies for co-occurring PTSD developed and tested, but these treatments have not been found effective versus comparison conditions, have moderate to poor retention rates, and have not been integrated within existing addiction treatment services or delivered by typical community addiction counselors. The present proposal builds upon a series of completed Stage I studies by the principal investigator, implementing a cognitive behavioral therapy (CBT) for PTSD in addiction treatment programs. The cumulative findings of the Stage I studies thus far demonstrate the CBT for PTSD to have promising effects on PTSD symptoms, substance use, and good retention rates (65-70 percent). This present research proposes a Stage II efficacy study of 228 participants recruited across seven typical community addiction treatment programs, and randomized to: a) CBT for PTSD + treatment-as-usual; b) Individual Addiction Counseling (IAC) + treatment-as-usual; or c) Treatment-as-usual alone. Community addiction counselors will deliver all treatments. Primary outcomes assessed at baseline, 3- and 6-months are: PTSD symptom severity, substance use severity and retention. The proposed research has the potential for significant impact by advancing a behavioral therapy that can reduce drug and alcohol use, attend to comorbid psychiatric conditions, and consider, a priori, translation to routine community settings and providers. This Stage II research capitalizes on the experience of the research team with a promising treatment, as found in the Stage I research activities. In addition, the research team has a track record of productive research relationships with typical community addiction treatment programs composed of routine addiction counselors and patients. Research within these settings should serve to enhance external validity and facilitate the translation of effective research-based treatments into the community.